High octane gasoline manufacture



United States Patent 0,"

r 2,908,629 Bron OCTANEIGASOLINE MANUFACTURE invention relates to theproduction of high octane gasolines; and more particularly to acombination process for. the treatment of a straight-run naphtha whereinthe. naphtha issubjected first to a reforming operation in the presenceof a dualfunction dehydrogenation-isomerization catalyst, and is thencatalytically cracked to convert low octane paraflins to normally liquidhigher octane compoundsor tonormally gaseous olefins capable of beingpolymerized to a high octane gasoline fraction.

Conventiona1 catalytic reforming of a straight-run petroleum fraction inthe gasoline boiling range, having an initial octane number below 60,will yield a product having an octane number in the range of 80 to 90,which can ,be upped toabout 88 to 95 by the addition of small amounts.of tetraethyl lead. While gasoline of this quality will satisfy mostpresent-day automobiles, the trend is toward higher compression motors,which have octane demands approaching 100 ON. It is therefore necessarythat processesbe developed which will enable apetrole um refiner toproduce gasoline of this quality in high yields. The principal object ofthis invention is to provide such a process.

, In accordance with the present invention, a straightrun gasolineboiling over the full gasoline boiling range, say from about 90 F. toabout 400 F., is subjected to the action of a dual-function reformingcatalyst at a temperature of from about 850 F. to about 975 F.; atpressures of from about 200 p.s.i.g. to about 600 p.s.i.g.; and in thepresence of from about 1 to about mols of added hydrogen per mol ofhydrocarbon. The dualfunction catalyst, which is essential in theprocess, is preferably platinum deposited on a base which has hightemperature acidic characteristics, such as alumina containing fromabout 0.3 to about 3 percent combined fluorine. Other acidic bases whichare suitable for use in practicing my invention include syntheticsilica-alumina, boria-alurnina and acid treated naturally occurringclays. Under the'foregoing conditions, the platinum component of thec'atalyst promotes dehydrogenation of naphthenes to. the ct'n'respondingaromatics, while the acidic component among other things promotesisomerization of parafiins to more highly branched structures. If thecatalyst contains-no acidic component as in the case where the catalystcomprises platinum or VI group metal oxides deposited on alumina alone,the paraflins contained in the feed will be subjected to somehydrocracking, but the majority will pass through the reforming stepuntouched, and will appear in the liquid product as straightchain oronly moderately branched compounds, which, for reasons which will behereinafter pointed out are undesirable.

The liquid product from the reforming step is then passed to a crackingzone in which it is subjected to the action of a cracking catalyst suchas synthetic silicaalurnina, bauxite, or certain naturally occurringclays. Temperature in the cracking zone should be from about 850"-F. to975? F., and the space velocity (volume of feed/volume of reactor/hr.)shouldbe from about 0.5 to 2. It has been found that under theseconditions the branched chain parafiins will be rather easily cracked tolow-boiling olefins, Such as' propylene, n-butylenes, and isobutylene,whereas the aromatics, being much more refractory, will pass throughunchanged, except for removing some of the alkyl side chains of three ormore carbon atoms. I have found that branched chain paraflins arecatalytically cracked with considerably less difficulty than straightchain paraffins, and that the yields of polymerizable gaseous olefinsare much higher, under the same operating conditions, if the feed to thecracking zone contains a large amount of branched chain parafli ns thanif the paraffin content is largely straight chain as would be the casewhen a non-acidic catalyst base is used in the reforming step. Moreover,the C olefins;

- formed will comprise considerably more 'isobutylene,

which forms a more valuable feed to a polymerizerthan the normalbutylenes. For this reason, as has been stated above, isomerization ofthe feed paraffins to more highly branched structures by the use of anacidic support for,

j the platinum catalyst in the reforming step, goes to the of balancedvolatility.

In order that those skilled in the art may more fully understand thenature of my invention and the I zone, the cyclohexanes inthe feed willbe dehydrogenated to the corresponding aromatics, the alkylcyclopentanes: will be largely isomerized to cyclohexanes anddehydroessence of the present invention.

The products of the cracking step are thenfractionated, to take overheada C and lower fraction, and a C Since a good proportion of theparaffinsin the feed to the cracking Zone are cracked therefraction as bottoms.

in to C and C hydrocarbons, While the aromatic con.- tent is virtuallyuntouched, the concentration of aromatics in this product will beconsiderably higher than in the feed, with accompanying increaseinoctanenumber. A

.higher octane number is also favored by the catalytic cracking ofhigher-boiling, low octane number, paraflins to lower-boiling C branchedchain parafiins and olefins,

of increased octane number.

.. The C and C fraction taken off as overhead in the fractionation maythen be polymerized in known'fashion to make a high octane numbergasoline, which is then combined with the aromatic bottom fraction, andwith an appropriate amount of extraneous butanes or other 3 high octanegasoline blending stocks to form a finished method of carrying it out,it will be more fully described in connection withthe accompanyingdrawing, which is a diagrammatic flow sheet of the process, certainprocess equipment, such as pumps, valves, etc., being omitted for v thesake of simplicity and clarity.

. As may be observed from the drawing, a feed stock, which may be'astraight-run naphtha boiling from FJto about 400 F. or a selectedfraction thereof, is taken from storage through line- 1, and is mixedwith a recycle hydrogen stream introduced through line 2. The

mixture is then passed through a furnace 3 in which it is heated to atemperature of from about 850 F. to about. 975 F., preferably from about900 F. to about 925 F. From furnace 3 the mixture is taken through line4, at a;

pressure of from about 200 p.s.i.g. to about 600 p.s.i.g. (preferablyabout 400 p.s.i.g.) and is passed to a reform? iug zone 5, which'ispacked with a catalyst comprising platinum supported on afluorine-containing alumina.

The method for preparing such a catalyst is fully de-- scribed in U.S.Patent 2,479,110 to Haensel, so that further' description of thecatalyst is deemed unnecessary here. Under the conditions prevailing inthe reforming genated to aromatics, and a large part of the parafiinswill Patented Oct. 13, 1959.

cracking is minimized, thus assuring a product.

Reaction products are removed from reforming zone 5 through line 6 andare passed to separator 7 from which hydrogen-containing gases areremoved overhead. A sufiicient amount of this gas is recycled to theprocess through line 2 to maintain the mol ratio of hydrogen tohydrocarbon in the feed to the reforming zone at a value of from about1:1 to about 10:1; excess hydrogen produced in the process being ventedfrom the system through line 8. The balance of the reformate, which willhave an octane number of between about 80 and 90, depending on theinitial octane number of the feed and upon the severity of the operatingconditions in reforming zone 5, is then taken through line 9 to furnace10, in which it is heated to a temperature of from about 850 F. to about975 F., and preferably to about 900 F., and isthen passed through line11 to a catalytic cracking zone 12. p

The cracking process utilized in catalytic cracking zone "12 may be ofany conventional type, such as fixed bed, moving bed, or fluid, andwill, of course, include facilties for the regeneration of catalystcontained therein. The catalyst may be any conventional crackingcatalyst, such as a synthetic silica-alumina gel, bauxite, or naturallyoccurring clays. The feed to cracking zone 12 is admitted thereto at arate such that its average residence time therein is sufiicient topermit the cracking of a large part of the paraffin content tolow-boiling olefins, while avoiding any appreciable demethylation ofaromatics. Normally the space velocity (liquid volume of feed/volume ofcatalyst/ hour) will be from about 0.5 to about 2.

Cracked products are withdrawn from cracking zone 12 through line 13 andare passed to fractionator'14, from which ethane and lower-boilinghydrocarbons are drawn oil overhead through line 15 for use as fuel orfor such other disposal as may be desired. Bottoms from fractionator 14are withdrawn through line 16 and are passed to fractionator 17 fromwhich a C -C fraction containing a high percentage of olefins is removedoverhead through line 18. A Q, and higher hydrocarbon fraction, which,due to the removal of parafiins by selective cracking is richer inaromatics than the feed to cracking zone 12, is removed fromfractionator 17 through line 19. This traction will have an octanenumber (F-1 clear) of from 95 to 100 or over depending on the severityof conditions in the cracking zone.

The C C fraction removed from fractionator 17 is passed to apolymerization zone 20 in which it is contacted with a polymerizationcatalyst such as sulphuric or phosphoric acid at standard polymerizationconditions well known to the art. Reaction products from polymerizationzone 20 are passed through line 21 to fractionator 22, from whichunreacted normally gaseous hy drocarbons are withdrawn overhead throughline 23. A high octane polymer gasoline is withdrawn from fractionator22 through line 24 and is combined with the bottoms from fractionator17. If desired, of course, the polymer gasoline may, instead of beingcombined with the aromatic fraction, be used for blending with otherlower octane number refinery stocks. Similarly, the aromatic fraction isuseful as gasoline per se, or for blending with other stocks.

As may be observed from the foregoing, I have devised a process for theproduction of high octane gasoline from low octane straight-run naphthain which there is a minimum loss to gaseous hydrocarbons. Sinceconditions in reforming zone 5 are such as to minimize hydrocracking,the loss in this step will be chiefly hydrogen produced in thedehydrogenation of naphthenes, and since conditions in catalyticcracking zone 12 are such as to minimize demethylation of aromatics,there will be .very little loss to C and lower hydrocarbons in thisstep, since the normally gaseous products from catalytic cracking arechiefly C and C hydrocarbons. The C and C; hydrohighyield of liquid 4carbons produced in the cracking step are largely olefinic so that theymay be converted into polymer gasoline to recover an ultimate high yieldof high octane gasoline.

While my new process may bear some superficial resemblance to some ofthe processes of the prior art, upon closer examination it will beapparent that it is clearly distinguishable from the most pertinent art,and that superior results are obtained by proceeding in accordancetherewith. For example, Voorhies in U.S. Patent 2,361,138, hydroforms astraight-run naphtha, and catalytically cracks that portion of thehydroformate boiling above 300 F., to recover material boiling in theaviation gasoline range, which is blended with the hydroformate boilingbelow 300 F. The catalyst used in the reforming step is molybdenumoxide, which does not promote paraifin isomerization. Thus Voorhiesgasoline product contains a considerable proportion of paraflins,largely straight chain or only moderately branched, boiling below 300 F.While these paraffins have a higher octane number than paraffins boilingabove 300 F., they have an octane number considerably below the octanenumber of the isoparaflins plus the polymer gasoline in the finalproduct made according to the present invention, and

is subjected to the cracking step.

In Welty U.S. Patent No. 2,490,287, a naphtha is reformed over amolybdenum oxide catalyst, and the reformate is subjected to thermalreforming, apparently to isomerize the paratlins. While the octanenumber is thereby improved, only a minor concentration of the aromatics,by destruction of paraffins, is obtained, with the production of anegligible quantity of low-boiling olefins, suitable for processing intohigh octane polymer gasoline. C and C hydrocarbons, which are lost touncondensible gases, than catalytic cracking.

It will thus be seen that, while useful two step proc, esses for thetreatment of straight-run naphthas, involving reforming in one step andcracking in the other, are broadly old, my invention is an improvementover previously proposed processes. This improvement resides in theconcept that by treatment of the naphtha with" a dual-functiondehydrogenation-isomerization catalyst in the first step of my process,it is possible to convert the parailins in the feed to branched chainstructures which are easily catalytically cracked to olefins, suitablefor further processing to polymer gasoline, under conditions such thatthe aromatics in the feed to the cracking step are largely unconverted.Cracking of the paraflins in this manner not only produces a suitablefeed stock for polymerization, but also results in an increasedconcentration of aromatics in the liquid product from the cracking step,with resultant very high octane number, and the combination of thisproduct with the polymer gasoline formed in the process yields agasoline with a yield/ octane relationship superior to any of the priorart two stage processes.

' it will be appreciated that While certain preferred temperatures andpressures have been set forth above, the optimum temperatures andpressures may vary somewhat, depending on the composition of'the feed toeach step. For example, if the feed to the reforming step is afull-boiling range naphtha the operating conditions should be somewhatmore severe than when charging a Furthermore, in the present process theentire' reformate, rather than the higher boiling fraction thereof,

Furthermore, thermal cracking makes morefraction having an initialboiling point of say 250 F. Similarly, optimum temperatures in thecracking step will depend to some extent on the degree of parafiinisomerization obtained in the reforming step. In general, however, theprocess is operable over the full extent of the wider temperature andpressure ranges given above.

The invention claimed is:

1. A process for the production of high octane gasoline which comprisespassing a straight-run naphtha boiling Within the gasoline boiling rangeto a reforming zone, therein subjecting said naphtha to the action of adualfunction dehydrogenation-isomerization catalyst at a temperature offrom 850 F. to 975 F., at a pressure of from 200 p.s.i.g. to 600p.s.i.g. and in the presence of added hydrogen, separating a normallyliquid product from the efiluent from the reforming zone; passing saidnormally liquid product to -a catalytic cracking zone and subjecting ittherein to the action of a cracking catalyst selected from the groupconsisting of synthetic silica-alumina gel, bauxite, andnaturally-occurring clays, in the absence of added hydrogen, at atemperature of from 850 F. to 975 F., and at a liquid hourly spacevelocity of 0.5 to 2, the temperature and space rate being correlated toproduce a cracking severity insutficient to substantially demethylatearomatics; recovering a second reaction product from the catalyticcracking zone, and fractionating the second reaction product to recovera C -C fraction comprising olefins, and a higher boiling fraction richin aromatics.

2. The process according to claim 1 in which the dualtunctiondehydrogenation-isomerization catalyst comprises platinum deposited onalumina containing from about 0.3 to about 3.0 percent combinedfluorine.

References Cited in the file of this patent UNITED STATES PATENTS2,361,138 Voorhies Oct. 24, 1944 2,380,279 Welty July 10, 1945 2,383,072Oblad Aug. 21, 1945 2,399,781 Arnold May 7, 1946 2,479,110 Haensel Aug.16, 1949 2,573,149 Kassel Oct. 30, 1951 2,596,145 Grote May 13, 19522,678,263 Glazier May 11, 1954 2,678,904 Kearby et a1. May 18, 19542,703,308 Oblad et a1. Mar. 5,. 1955 2,758,062 Arundale et a1. Aug. 7,1956 2,767,124 Myers Oct. 16, 1956 2,775,638 Milliken et a1. Dec. 25,1956 2,780,661 Hemminger et al. Feb. 5, 1957 lishing Co., N.Y., 2nd ed.(1948) (pages 387 and 418 relied on).

1. A PROCESS FRO THE PRODUCTION OF HIGH OCTANE GASOLINE WHICH COMPRISESPASSING A STRAIGHT-RUM NAPHTHA BOILING WITHIN THE GASOLINE BOILING RANGETO A REFORMING ZONE, THEREIN SUBJECTING SAID NAPHTHA TO THE ACTION OF ADUALFUNCTION DEHYDROGENATION-SIOMERIZATION CATALYST AT A TEMPERATURE OFFORM 850*F. TO 975*F., AT A PESSURE OF FROM 200 P.S.I.G. TO 600 P.S.I.G.AND IN THE PRESENCE OF ADDED HYDROGEN, SEPARATING A NORMALLY LIQUIDPRODUCT FROM THE EFFLUENT FROM THE REFORMING ZONE; PASSING SAID NORMALLYLIQUID PRODUCT TO A CATALYTIC CRACKING ZONE AND SUBJECTING IT THEREIN TOTHE ACTION OF A CRACKING CATRALYST SELECTED FROM THE GROUP CONSISTING OFSYNTHETIC SILICA-ALUMINA GEL, BAUXITE, AND NATURALLY-OCCURRING CLAYS, INTHE ABSENCE OF ADDED HYDROGEN, AT A TEMPERATURE OF FROM 850*F. TO975*F., AND AT A LIQUID HOURLY SPACE VELOCITY OF 0.5 TO 2, THETEMPERATURE AND SPACE RATE BEIG CORRELATED TO PRODUCE A CRACKINGSEVERITY INSUFFICIENT TO SUBSTANTIALLY DEMETHLYLATE AROMATICS;RECOVERING A SECOND REACTION PRODUCT FROM THE CATALYTIC CRACKING ZONE,AND FRACTIONATING THE SECOND REACTION PRODUCT TO RECOVER A C3-C4FRACTION COMPRISING OLEFINS, AND A HIGHER BOILING FRACTION RICH INAROMATICS.